Solid state conductive polymer compositions

ABSTRACT

Solid state conductive polymer compositions which are ionically-conductive regardless of the amount of water present in the composition are disclosed. The compositions have solvating polymer, ionic salt, and optionally if the composition is not cohesive and pliable, essentially non-volatile plasticizer in an amount sufficient to render the composition cohesive and pliable. Biomedical electrodes having means for electrical communication contacting the compositions are also disclosed. Methods of making the compositions and electrodes are also disclosed.

This is a continuation of application Ser. No. 08/101,812 filed Jul. 30,1993 now U.S. Pat. No. 5,385,679, which is a continuation of Ser. No.07/792,597 filed Nov. 15, 1991, abandoned.

FIELD OF THE INVENTION

This invention relates to solid state conductive polymer compositionswhich are ionically-conductive regardless of the amount of water presentin the composition, biomedical electrodes containing such compositions,and a method of preparing such compositions.

BACKGROUND OF THE INVENTION

Modern medicine uses many diagnostic, therapeutic, and electrosurgicalprocedures where electrical signals or currents are received from ordelivered to a patient's body. The interface between medical equipmentused in these procedures and the skin of the patient is usually somesort of biomedical electrode. Such an electrode typically includes aconductor which must be connected electrically to the equipment, and aconductive medium adhered to or otherwise contacting skin of a patient.

Among the therapeutic procedures using biomedical electrodes aretranscutaneous electronic nerve stimulation (TENS) devices used for painmanagement; neuromuscular stimulation (NMS) used for treating conditionssuch as scoliosis; defibrillation electrodes to dispense electricalenergy to a chest cavity of a mammalian patient to defibrillate heartbeats of the patient; and dispersive electrodes to receive electricalenergy dispensed into an incision made during electro surgery.

Among diagnostic procedures using biomedical electrodes are monitors ofelectrical output from body functions, such as electrocardiogram (ECG)for monitoring heart activity and for diagnosing heart abnormalities.

For each diagnostic, therapeutic, or electrosurgical procedure, at leastone biomedical electrode having an ionically-conductive mediumcontaining an electrolyte is adhered to or otherwise contactingmammalian skin at a location of interest and also electrically connectedto electrical diagnostic, therapeutic, or electrosurgical equipment. Acritical component of the biomedical electrode is the conductive mediumserving as the interface between mammalian skin and diagnostic,therapeutic, or electrosurgical equipment.

The conductive medium conventionally employed in biomedical electrodesutilizes one of two classes of polymer conductive materials: gelelectrolytes or polyelectrolytes. Both gel electrolytes andpolyelectrolytes are ionically-conductive polymer systems in the form ofconductive gels, creams, and conductive adhesives.

As discussed in Chapter 6, "Mixed Polymer Systems" by F. M. Gray inMacCallum, Ed., Polymer Electrolyte Reviews I, Elsevier Applied Science,New York (1987), at pages 139-141 gel electrolytes have been defined aspolymer-solvent-salt systems which the role of the polymer is secondaryin the conducting matrix. The polymer serves as a thickener for lowmolecular weight, high dielectric constant solvents which solvate thesalt and act as the conducting medium.

The solvent can be either an aqueous solution or a co-solvent consistingof water and a polyhydric alcohol. U.S. Pat. No. 4,406,827 (Carim)describes the utilization of gel electrolyte in biomedical electrodes,in which a guar gum network serves as a matrix to confine a solution ofpotassium chloride. To function properly, the conductive guar gum gelelectrolyte system requires the presence of water. Unfortunately, gelelectrolyte systems are susceptible to dehydration of the essentialwater needed to maintain ionic conductivity.

Also as discussed by Gray at pages 139-141, a polyelectrolyte is aconductive matrix formed by the dissolution of an ionic polymer in anaqueous medium. Ionic polymers are hybrids of ionic salts and covalentpolymers, and can have structural features common to both.

Again, water is a necessary component to the polymer system, in order todissociate ions of the ionic polymer and to plasticize the polymer toincrease ionic mobility. Ionic conductivity of a polyelectrolyte is afunction of the amount of water content. U.S. Pat. No. 4,524,087 (Engel)describes a biomedical electrode employing a polyelectrolyte polymerconductive material. In this instance, the polyelectrolyte is aconductive adhesive consisting of a partially neutralized polyacrylicacid homopolymer dispersed in water and glycerin. Unfortunately,polyelectrolyte-containing biomedical electrodes are also susceptible todehydration of water which reduces ionic conductivity of the polymer.

The loss of water from biomedical electrodes using either gelelectrolytes or polyelectrolytes has been an unresolved problem. Despiteefforts to provide packaging which stabilizes the water vapor pressureof a biomedical electrode within a package, once a biomedical electrodeis exposed to the general atmosphere, dehydration commences, resultingin unacceptable electrical properties. In the case of polyelectrolytes,having adhesive properties, dehydration also results in decreasingadhesion of the electrode to mammalian skin.

An approach to making a dry polyelectrolyte biomedical electrode isdisclosed in U.S. Pat. No. 5,003,978 (Dunsheath, Jr.) where a conductiveadhesive is coated on a conductive substrate. The substrate is composedof polymer materials having finely ground powders loaded therein. Theconductive adhesive is composed of a water-based adhesive having adiffusion of chloride ions throughout the adhesive. Water in theadhesive is less than 5% by weight.

Another approach to making a dry polyelectrolyte biomedical electrode isdisclosed in U.S. Pat. No. 4,273,135 (Larimore et al.). The conductivematerial consists essentially of a cohesive, conformable, nonionichydrophilic synthetic polymer including non-ionic water-soluble polymersof substantially all water soluble monomers which is plasticized withagents compatible with the polymer. At the time of application of anelectrode, skin of a patient is lightly abraded and dampened with wateror normal saline solution to provide electrolytic conductivity. Thus,water or an aqueous solution is required for use even if the electrodeis dry during storage.

A third class of polymer conductive materials is known and the subjectof MacCallum, Ed., Polymer Electrolyte Reviews I, described above, andspecifically Chapters 5 and 6 by Gray therein. These materials arecalled polymer electrolytes, which are ionically-conductive polymermaterials where ionic salts are dissolved directly into a solvatingpolymer matrix. Therefore, direct interaction between non-carbon atomsin the polymer backbone of the polymer and the cation of the salt yieldsa conductive solid solution.

One conductive polymer electrolyte having high ionic conduction isdisclosed in U.S. Pat. No. 4,855,077 (Shikinami et al.). In thisinstance, the polymeric ionic conductor is composed of segmentedpolyurethane having polyethylene oxide, polypropylene oxide, etc. in thesegments thereof and having a high ionic conduction by a complex formedby the segment and an ionic compound. The use of a polyalkylene oxideachieves a polymer which has an amorphous phase aggregate almost all orcompletely all of which is in the rubbery state because the glasstransition temperature of the polyalkylene oxide is lower than roomtemperature. Thus, the polymer can become a material with stickingproperty and can include a plasticizer added thereto for imparting tack.However, Shikanami et al. require the polymerization of a polyurethanefrom prepolymers using organic solvent systems, which could leaveresidual oligomeric units in the final product.

SUMMARY OF THE INVENTION

The present invention achieves a solid state conductive polymercomposition which is ionically-conductive regardless of the amount ofwater present during manufacture, storage or use. Solid state conductivepolymer compositions of the present invention are not susceptible to aloss of conductivity due to dehydration of water or other volatilecomponents after manufacture and prior to completion of use. Nor is theconductivity of such compositions impaired by the absorption of waterinto such compositions in humid atmospheric conditions.

Compositions of the present invention can be made with minimal amountsof water present during manufacture. Such compositions can be stored inhumid or arid conditions without protection from atmospheric moisture.Such compositions can be used without regard to the amount ofatmospheric moisture or body fluids or exudate likely to be encounteredduring diagnostic, therapeutic, or electrosurgical procedures. In short,compositions of the present invention solve the problem of requiringwater to achieve ionical conductivity in compositions in biomedicalelectrodes which contact mammalian skin. Compositions of the presentinvention function independently of the presence or absence of water.Water is accommodated in such compositions, but not required for use.

Solid state conductive polymer compositions of the present invention canbe used as the conductive medium in a biomedical electrode conductivelyinterfacing between mammalian skin and means for electricalcommunication to electrical diagnostic, therapeutic, or electrosurgicalequipment.

A solid state conductive polymer composition ionically-conductiveregardless of an amount of water present in the composition comprises apolymer electrolyte complex and optionally if the complex is notcohesive and pliable, an essentially non-volatile plasticizer in anamount sufficient to render the composition cohesive and pliable. Apolymer electrolyte complex comprises a solid solution of ionic saltdissolved in a solvating polymer. A conductive solid solution isachieved through dissociation of ionic salts by a solvating polymer,forming a cation-polymer complex and its counterion. The cation-polymercomplex occurs with direct interaction of non-carbon atoms in thepolymer chain.

A solvating polymer can be either a homopolymer where each monomericunit has at least one ionizing non-carbon atom or a copolymer where atleast one monomeric unit has at least one ionizing non-carbon atomcontained in a pendant group to the monomeric unit.

The invention also achieves the use of a solid state conductive polymercomposition described above as a conductive medium in a biomedicalelectrode.

A biomedical electrode comprises a conductive medium, a solid stateconductive polymer composition described above and means for electricalcommunication interacting between the conductive medium and electricaldiagnostic, therapeutic, or electrosurgical equipment.

It is a feature of the present invention that no water or other volatileplasticizer is required to insure ionic conductivity in a solid stateconductive polymer composition of the present invention.

It is another feature of the invention that solid state conductivepolymer compositions of the present invention can use plasticizers whichare essentially non-volatile at ambient conditions.

It is another feature of the present invention that biomedicalelectrodes containing solid state conductive polymer compositions of thepresent invention are not susceptible or otherwise sensitive todehydration or evaporation of other volatile liquid.

It is another feature of the present invention that biomedicalelectrodes containing solid state conductive polymer compositions of thepresent invention can be stored in open containers to the atmosphere,requiring fewer packaging limitations than presently required forbiomedical electrodes requiring the presence of water for ionicconductivity.

It is an advantage of the invention that solid state conductive polymercompositions of the present invention can be plasticized to provide abroad scope of conductive materials, ranging from non-volatile gels andcreams to non-volatile conductive adhesives.

It is another advantage of the present invention that more consistentimpedance can be achieved during use in diagnostic procedures becausebiomedical electrodes containing solid state conductive polymercompositions of the present invention function regardless of the amountof water or polar solvent present in the composition.

It is another advantage of the present invention that use of biomedicalelectrodes having compositions of the present invention do not requirespecial skin preparations prior to use. Indeed the absence of waterreduces the incidence of a "cold" feeling when a biomedical electrode ofthe present invention contacts mammalian skin.

It is another advantage of the present invention that compositions ofthe present invention can provide ionic conductivity as an extremelythin coating on a means for electrical communication for a biomedicalelectrode. Thus, biomedical electrodes of the present invention can havea low profile and can be conformable to a variety of contours onmammalian skin. Another aspect of the present invention is the ease bywhich solid state conductive polymer compositions of the presentinvention can be made. A method of preparing a non-volatile, solid stateconductive polymer composition comprises mixing a solvating polymer, anionic salt, and an essentially non-volatile plasticizer, if any isneeded to render the composition cohesive and pliable, into anessentially volatile solvent and removing solvent to form a non-volatilesolid state conductive polymer composition regardless of an amount ofwater present in the composition.

Evaporation is a preferred method of reducing the amount of essentiallyvolatile solvent for manufacturing efficiency. The extent of evaporatingcan be adjusted according to preferences of one skilled in the art.Because solid state conductive polymer compositions of the presentinvention maintain conductivity regardless of the amount of waterpresent in the composition, it is preferred to nearly completelyevaporate such volatile solvent when making compositions of the presentinvention.

It is a feature of that aspect of the present invention that a method ofpreparing solid state conductive polymer compositions of the presentinvention do not require, but can accommodate the continued presence ofessentially volatile liquids in the composition.

It is another feature of the present invention that a solid stateconductive polymer composition can be made in an extremely thin coatingof less than about 0.25 mm on a substrate, preferably a substrate withan electrically conductive surface.

It is another feature of the present invention that a solid stateconductive polymer composition can be made using a volatile solvent suchas water which is environmentally preferred.

It is an advantage of the present invention that a method of preparingsolid state conductive polymer compositions of the present invention canbe achieved with a minimum number of steps employing ecologicallycompatible materials.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a top plan view of a biomedical electrode containing a solidstate conductive polymer composition of the present invention.

FIG. 2 is a sectional view of the biomedical electrode of FIG. 1.

FIG. 3 is a perspective view of a dispersive biomedical electrode usedfor receiving electrical current during electrosurgery.

FIG. 4 is a cross-sectional view of the dispersive biomedical electrodeof FIG. 3.

EMBODIMENTS OF THE INVENTION Solvating Polymer

Solvating polymers useful in solid state conductive polymer compositionsof the present invention can be either a homopolymer where eachmonomeric unit has at least one ionizing non-carbon atom or a copolymerwhere at least one monomeric unit has at least one ionizing non-carbonatom contained in a pendant group to the monomeric unit. Nonlimitingexamples of a non-carbon atom in a monomeric unit include oxygen,nitrogen, sulphur, and phosphorus.

Of possible solvating polymers, poly(N-vinyl lactam); polyacrylamide orits ionic forms; polyacrylic acid or its salts; poly(vinyl alcohol)prepared from hydrolyzing polyvinyl acetate; poly(vinyl methyl ether);poly(2-acrylamido-2-methylpropanesulfonic acid), its salts, copolymersof the acid, copolymers of salts of the acid, or mixtures thereof; orcombinations of these solvating polymers are useful. Of these possiblesolvating polymers, crosslinked poly(N-vinyl lactam); crosslinkedpolyacrylamide; crosslinked polyacrylic acid or its salts; crosslinkedpoly(acrylamido-2-methylpropanesulfonic acid), its salts, crosslinkedcopolymers of the acid, crosslinked copolymers of salts of the acid ormixtures thereof; or combination of these crosslinked solvating polymersare preferred. Of these preferred solvating polymers, a crosslinkedpoly(N-vinyl lactam) is especially preferred.

Solvating polymer can be present in a conductive polymer composition inan amount from about 5 to 98 weight percent. In a composition in which aplasticizer is added to render the composition cohesive and pliable, thesolvating polymer can comprise from about 5 to about 50 weight percent,and preferably from about 20 to about 45 weight percent, of theconductive polymer composition.

Poly(N-vinyl lactam) can be a noncrosslinked homopolymer or anoncrosslinked copolymer containing N-vinyl lactam monomeric units,which after crosslinking, such as by irradiation, is swellable in aplasticizer biocompatible with mammalian skin.

Preferably, noncrosslinked homopolymer or noncrosslinked copolymer issoluble in plasticizer biocompatible with mammalian skin in the absenceradiation crosslinking. N-vinyl lactam monomeric units comprise amajority of total monomeric units of the polymer.

Nonlimiting examples of N-vinyl lactam monomers areN-vinyl-2-pyrrolidone; N-vinyl-2-valerolactam; N-vinyl-2-caprolactam;and mixtures of any of the foregoing. Preferably, the N-vinyl lactam isN-vinyl- 2-pyrrolidone. Preferably, the poly(N-vinyl lactam) is ahomopolymer of N-vinyl-2-pyrrolidone.

Nonlimiting examples of non-N-vinyl lactam comonomers useful withN-vinyl lactam monomeric units include N,N-dimethylacrylamide, acrylicacid, methacrylic acid, hydroxyethylmethacrylate, acrylamide,2-acrylamido-2-methyl-1-propane sulfonic acid or its salt, and vinylacetate.

The N-vinyl lactam monomeric units comprise no less than about 50 weightpercent of the monomeric units present in the poly(N-vinyl lactam) insolid state form. More preferably, the N-vinyl lactam monomeric unitscomprise 70 to 100 percent by weight of the poly(N-vinyl lactam) andmost preferably 90 to 100 percent by weight of the poly(N-vinyl lactam).

Noncrosslinked poly(N-vinyl lactam) homopolymer and poly(N-vinylpyrrolidone)/poly vinyl acetate copolymers are commercially available.Nonlimiting examples of commercially available poly(N-vinyl pyrrolidone)useful for the present invention include Aldrich Chemical Co. ofWilwaukee, Wis., BASF of Parsippany, N.J., and GAF of Wayne, N.J.

Poly(N-vinyl lactam) can have a Fikentscher K-value of at least K-15 andpreferably at least K-60, and most preferably at least K-90. FikentscherK-values are described in Molyneaux, Water-Soluble Polymers: Propertiesand Behavior, Vol. 1, CRC Press, 1983, pp. 151-152.

After exposure to ionizing radiation, poly(N-vinyl lactam) can have aSwelling Capacity, S, milliliters of liquid sorbed per gram of polymer,of at least about 15 in water, preferably about 20-35 in water, and mostpreferably about 25 in water.

Swelling Capacity correlates to a measurement of polymer swelling as afunction of chemical crosslinking units in poly(N-vinyl lactam),according to the equation:

    S=C(λ.sup.1/3 -λ.sub.o.sup.1/3)

where S is a measurement of water sorbed per gram of polymer, C is aconstant characteristic of the polymer, i.e., milliliters of watersorbed per gram of polymer, λ is the average number of backbone atoms inthe polymer segments between crosslinked junctions, and λ_(o) is theaverage number of backbone carbon atoms in the polymer segments betweencrosslinked junctions when S is zero. Swelling capacity and thisequation are discussed in Errede, "Molecular Interpretations of Sorptionin Polymers Part I" Advances in Polymer Science Vol. 99,Springer-Verlag, Berlin Heidelberg Germany (pp. 21-36, 1991), thedisclosure of which is incorporated by reference.

Poly(N-vinyl lactam) useful in the present invention can be in any formsusceptible to being crosslinked, but preferably is in a solid stateform. Nonlimiting examples of solid state forms include particles,pellets, sheets, strands, fibers, membranes, films, and other threedimensional functional forms. Preferably, poly(N-vinyl lactam) is in theform of particles of a size from about 0.1 micrometers to about 250micrometers and preferably from about 10 micrometers to about 75micrometers.

Crosslinked poly(N-vinyl lactam) compositions can be prepared usingfree-radical polymerization methods employing chemical crosslinkingagents such as that disclosed in U.S. Pat. No. 4,848,353 (Engel) or EPOPublication 0 322 098 (Duan) or using ionizing radiation such as thatdisclosed in U.S. Pat. No. 5,276,079 (Duan et al.), the disclosures ofsuch methods of crosslinking being incorporated by reference as ifrewritten herein.

Crosslinked polyacrylamide; crosslinked polyacrylic acid or its salts;crosslinked poly(2 -acrylamide-2-methylpropanesulfonic acid or itssalts, crosslinked copolymers of the acid, crosslinked copolymers ofsalts of the acid or mixtures thereof; or combinations thereof can beprepared by using free-radical polymerization methods known to thoseskilled in the art.

Essentially Non-volatile Plasticizer

If solid state conductive polymer compositions require a plasticizer torender the composition cohesive and pliable, and preferably pressuresensitive adhesive, the plasticizer can be an essentially non-volatileliquid or combination of liquids which can swell the solvating polymerand which is biocompatible with mammalian skin.

Essentially non-volatile means that a plasticizer as used in the presentinvention will render a polymer electrolyte complex of solvating polymerand ionic salt sufficiently cohesive and pliable such that less than tenpercent (10%) of a given volume of plasticizer evaporates after exposureto a temperature of processing the composition or to a temperature ofstorage conditions.

Non-limiting examples of essentially non-volatile plasticizers includepolyhydric alcohols (e.g., ethylene glycol, propylene glycol, sorbitol,polyethylene glycol, and glycerin) and other plasticizers which arenon-volatile in ambient conditions and do not cause mammalian skinirritation or toxic reaction.

Essentially non-volatile plasticizer can be added in an amountsufficient to render a solid state conductive polymer compositioncohesive and pliable, and preferably also pressure-sensitive adhesive.The amount of plasticizer to be added to form a cohesive, pliable, solidstate conductive pressure-sensitive adhesive depends on the type ofsolvating polymer employed and the extent of crosslinking in thesolvating polymer.

The essentially non-volatile plasticizer can be added to solvatingpolymer ranging from about 0 to about 95 weight percent of the solidstate conductive polymer composition. One can adjust the amount ofplasticizer employed to control adhesive properties of the polymerelectrolyte complex. Preferably, the amount of plasticizer added canrange from about 50 to 75 weight percent of the composition when thesolvating polymer is crosslinked poly(N-vinyl lactam). Preferably, theamount of plasticizer can range from about 65 to 75 weight percent ofthe composition when the solvating polymer is crosslinked polyacrylicacid; crosslinked polyacrylamide; or crosslinkedpoly(2-acrylamido-2-methylpropanesulfonic acid) or its salts,crosslinked copolymers of the acid, crosslinked copolymers of salts ofthe acid, or mixtures thereof.

Of essentially non-volatile plasticizers, glycerin and polyethyleneglycol are preferred, with polyethylene glycol most preferred. Glycerinand polyethylene glycol can be used in mixtures. Glycerin can compriseup to 100 weight percent of the essentially non-volatile plasticizer.Preferably, polyethylene glycol can comprise up to 100 weight percent ofthe essentially non-volatile plasticizer. Polyethylene glycol of either300 molecular weight or 400 molecular weight is preferred, with 300molecular weight more preferred.

Unexpectedly, solid state conductive polymer compositions of the presentinvention do not require the use of water, or the retention of water orany other volatile liquid capable of vaporization at ambient conditions,as a plasticizer for polymer electrolyte complex used in the presentinvention to provide ionic conductivity. By relying on essentiallynon-volatile plasticizers to render solid state conductive polymercompositions cohesive and pliable, and preferably pressure-sensitiveadhesive, biomedical electrodes employing such solid state conductivepolymer compositions are less apt to have ionic conductivity altered bydehydration of a component of the composition.

While solid state conductive polymer compositions of the presentinvention do not require water to be present, such compositions canaccommodate the presence of water in such composition without losingionic conductivity or adhesive performance. Thus, solid state conductivepolymer compositions of the present invention function regardless of theamount of water present during manufacture, storage, or use.

Ionic Salts

Solvating polymers contain one or more ionic salts in amounts sufficientto interact with non-carbon atoms of the solvating polymer in order toform polymer electrolyte complexes which can be plasticized to formsolid state conductive polymer compositions of the present invention. Ineffect, solid state conductive polymer composition is a matrix of (a) aconductive solid solution of one or more ionic salts dissociating in asolvating polymer and (b) an essentially non-volatile plasticizerpresent, if any, in an amount sufficient to render the matrix cohesiveand pliable, and preferably pressure-sensitive adhesive. Thus,unexpectedly, the interaction of ionic salts with the solvating polymerprovides ionic conductivity for the composition. Ionic or polar solventssuch as water previously employed in polyelectrolyte compositions arenot necessary to provide ionic conductivity in a conductive medium of abiomedical electrode.

Non-limiting examples of ionic salts useful for interaction with thesolvating polymer include lithium chloride, lithium perchlorate, sodiumcitrate, and preferably potassium chloride.

To provide acceptable ionic conductivity, ionic salts can be present inamounts from about 0.5 weight percent to about 5 weight percent of thesolid state conductive polymer composition. Preferably, ionic salts arepresent in amounts from about 2 to about 3 weight percent of the solidstate conductive polymer composition.

Biomedical Electrodes

Biomedical electrodes employing solid state conductive polymercompositions of the present invention are useful for diagnostic,therapeutic and electrosurgical purposes. In its most basic form, abiomedical electrode comprises a conductive medium contacting mammalianskin and a means for electrical communication interacting between theconductive medium and electrical diagnostic, therapeutic, orelectrosurgical equipment.

FIGS. 1 and 2 show either a disposable diagnostic electrocardiogram(EKG) or a transcutaneous electrical nerve stimulation (TENS) electrode10 on a release liner 12. Electrode 10 includes a field 14 of abiocompatible and adhesive conductive medium for contacting mammalianskin of a patient upon removal of protective release liner 12. Electrode10 includes means for electrical communication 16 comprising a conductormember having a conductive interface portion 18 contacting field 14 ofconductive medium and a tab portion 20 not contacting field 14 ofconductive medium for mechanical and electrical contact with electricalinstrumentation (not shown). Means 16 for electrical communicationincludes a conductive layer 26 coated on at least the side 22 contactingfield 14 of conductive medium.

It is foreseen that a typical EKG conductor member 16 will comprise astrip of material having a thickness of about 0.05-0.2 millimeters, suchas polyester film and have a coating 26 on side 22 of silver/silverchloride of about 2.5-12 micrometers, and preferably about 5 micrometersthick thereon. Presently preferred is a polyester film commerciallyavailable as "Mellinex" 505-300, 329, 339 film from ICI Americas ofHopewell, Va. coated with a silver/silver chloride ink commerciallyavailable as "R-300" ink from Ercon, Inc. of Waltham, Mass. A TENSconductor member 16 can be made of a non-woven web, such as a web ofpolyester/cellulose fibers commercially available as "Manniweb" web fromLydall, Inc. of Troy, N.Y. and have a carbon ink layer 26 commerciallyavailable as "SS24363" ink from Acheson Colloids Company of Port Huron,Mich. on side 22 thereof. To enhance mechanical contact between anelectrode clip (not shown) and conductor member 16, an adhesively-backedpolyethylene tape can be applied to tab portion 20 on the side oppositeside 22 having the conductive coating 26. A surgical tape commerciallyavailable from 3M Company as "Blenderm" tape can be employed for thispurpose.

Another type of therapeutic procedure, which can employ a biomedicalelectrode having a solid state conductive polymer composition of thepresent invention, is the dispensing of electrical energy to the chestcavity of a mammalian patient to defibrillate abnormal heart beats ofthe patient. Delivery of a high (e.g., 2000 volts) voltage, high (e.g.,40 amps) current electrical charge through one biomedical electrode andreceipt of that electrical charge through another biomedical electrodecompletes the electrical circuit. An example of an electrode useful fordefibrillation is disclosed in U.S. Pat. No. 3,998,215 (Anderson etal.), which is incorporated herein by reference.

Another type of therapeutic procedure involving application ofelectrical current to skin of a patient is iontophoresis, which deliversan iontophoretically active pharmaceutical to or through mammalian skinwith aid of an electrical current.

Another type of medical procedure employing a biomedical electrode usinga solid state conductive polymer composition of the present invention iselectrosurgery. In this instance, the biomedical electrode serves toreceive in a dispersed fashion electrical signals introduced to thepatient at an incision site using an electro-surgical cutting electrode.An electro-surgical system usually comprises a generator providinghigh-frequency alternating current on demand under monitored conditions,the cutting electrode having an extremely high-current density and aflat dispersive biomedical electrode having a very large surface area toprovide a low-current density. The dispersive biomedical electrode isplaced in intimate and continuous contact with a portion of themammalian skin which is not subject to the surgical procedure. Thealternating current circuit is completed through the body of the patientbetween the dispersive biomedical electrode and the cutting electrode.Disconnection of the dispersive electrode either from contacting thepatient or from the generator could subject the patient to electricalburns where the alternating current circuit leaves the body of thepatient.

A dispersive electrode is seen in FIGS. 3 and 4. Dispersive electrode 30comprises an insulating backing 31 coated on one surface with abiocompatible pressure sensitive adhesive 32. The backing 31 can be aclosed cell polyethylene foam. An electrode plate 33 adheres to aportion of the biocompatible pressure sensitive adhesive 32. Theelectrode plate 33 can be an aluminum foil or a conformable polymericbacking 34, e.g., polyester, having aluminum deposited on one surface.The electrode plate 33 has an integrally associated connector tab 35suited to electrically connect the dispersive electrode 30 to a leadwirewhich in use is connected to an electrosurgery generator. A field ofelectrically-conductive adhesive 36 of the present invention coats theentire electrically-conductive surface of electrode plate 33 except theconnector tab 35. An insulating strip 37 double coated with pressuresensitive adhesive covers that portion of the surface of the connectingtab 35 which underlies the backing 31 and biocompatible pressuresensitive adhesive 32. The backing 31 and biocompatible pressuresensitive adhesive 32 have an apron 38 extending beyond the periphery ofthe electrode plate 33 and electrically-conductive adhesive 36. Apron 38and insulating strip 37 serve to insulate the electrode plate 33 fromdirect contact with a patient's skin, thereby avoiding thermal burns,and from contact with other conductors (e.g., blood or water) which mayresult in an electrical short circuit. Supporting connecting tab 35 is areinforcing layer 39 of nonwoven polyester contating adhesive 32 andhaving a single coated adhesive layer contacting tab 35. An optionalrelease liner 40 can be used to protect adhesives 32 and 36 prior touse.

Preferably, to achieve excellent adhesion and electrical contact with apatient's skin (avoiding hot spots or loss of contract due to motion),surface area of plate 33 and adhesive 36 of the present invention areabout 130 cm². Preferably, the adhesive 36 of the present invention iscoated about 0.5 mm thick. Other examples of biomedical electrodes whichcan use solid state conductive polymer compositions of the presentinvention as conductive adhesive fields include electrodes disclosed inU.S. Pat. Nos. 4,527,087; 4,539,996; 4,554,924; 4,848,353 (all Engel);4,846,185 (Carim); 4,771,713 (Roberts); 4,715,382 (Strand); 5,012,810(Strand et al.); co-pending and co-assigned U.S. patent application Ser.No. 07/686,049; co-pending and co-assigned U.S. patent application Ser.No. 07/688,138, the disclosures of which are incorporated by referenceherein.

When used for diagnostic EKG procedures, electrodes shown in FIGS. 1 and2 are preferred. When used for monitoring electrocardiogram (ECG)procedures, electrodes disclosed in U.S. Pat. No. 5,012,810 andapplication Ser. No. 07/686,049 are preferred. When used fordefibrillation procedures or electrosurgical procedures, electrodesshown in FIGS. 3 and 4 or disclosed in U.S. Pat. No. 4,539,996 arepreferred.

In some instances, the means for electrical communication can be anelectrically conductive tab extending from the periphery of thebiomedical electrodes such as that seen in U.S. Pat. No. 4,848,353 orcan be a conductor member extending through a slit or seam in ainsulating backing member, such as that seen in U.S. Pat. No. 5,012,810.Otherwise, the means for electrical communication can be an eyelet orother snap-type connector such as that disclosed in U.S. Pat. No.4,846,185. Alternatively, an electrically conductive tab such as thatseen in U.S. Pat. No. 5,012,810 can have an eyelet or other snap-typeconnector secured thereto. Further, the means for electricalcommunication can be a lead wire such as that seen in U.S. Pat. No.4,771,783. Regardless of the type of means for electrical communicationemployed, preferably adhesive solid state conductive polymercompositions of the present invention can reside as a field ofconductive adhesive on a biomedical electrode for diagnostic,therapeutic, or electrosurgical purposes.

Method of Preparing Solid State Conductive Polymer Compositions

A method of preparing an essentially nonvolatile solid state conductivepolymer composition of the present invention can employ a minimum numberof ecologically compatible manufacturing steps. The solvating polymer,ionic salt, and essentially non-volatile plasticizer, if any as needed,are mixed into a solvent which is essentially volatile at or aboveambient temperatures, such as water, ethanol, methanol, isopropanol,acetone, heptane, and ethyl acetate. A quantity of the mixture ofsolvating polymer, ionic salt, and any essentially non-volatileplasticizer present in the volatile solvent is then cast onto a surfaceof a substrate, which can be an inert substrate such as a liner forstorage before further processing or a surface of a means for electricalcommunication having an electrically conductive surface. Then thevolatile solvent is essentially evaporated by the application of heat,microwave energy, infrared energy, convective air flow or the like, inorder to form the non-volatile solid state conductive polymercomposition on the substrate. Typically, a drying oven heated to about65° C. can be employed. A product liner can optionally be laminated overthe field of solid state conductive polymer composition to protect thatfield from contamination.

An extremely thin coating of solid state conductive polymer compositioncan be applied to a substrate surface. Coating thickness ranges fromabout 0.125 mm to about 1.25 mm and preferably from about 0.75 mm toabout 1 mm, to yield after evaporation of solvent a coating thicknessranging from about 0.05 mm to about 0.38 mm and preferably from about0.18 mm to about 0.25 mm. With this extremely thin coating of aconductive, and preferably adhesive, composition on a flexible,electrically conductive substrate, a low profile and conformablebiomedical electrode can be made.

Alternatively, solid state conductive polymer compositions of thepresent invention can be prepared from monomers and crosslinking agents,in a similar process to that described in U.S. Pat. No. 4,524,087(Engel), the disclosure of which is incorporated herein, using aphotoinitiator and a 15 watt blacklight operating about about 350 nmwavelength and 1.2 milliwatts/cm² intensity for about four minutes in anitrogen atmosphere. Because no water is required for the resultingsolid state conductive polymer composition, no water is added as a partof the process.

Compositions can be prepared in a batch process or in a continuous lineprocess. If prepared by a continuous process, the laminate of a liner,field of non-volatile solid state conductive polymer composition, andsubstrate can be wound on a roll for bulk packaging and furtherprocessing or can be cut using dies known to those skilled in the artinto individual electrodes or electrode subassemblies for furtherprocessing. U.S. Pat. No. 4,795,516 (Strand) and U.S. Pat. No. 4,798,642(Craighead et al.), which are incorporated by reference herein, discloseprocesses and equipment useful for a continuous manufacture ofbiomedical electrodes involving the dispensing of strips of materialfrom rolls and overlaying such strips in a registered continuous mannerin order to prepare a strip of electrodes. Further, co-pending,co-assigned U.S. patent application Ser. Nos. 07/686,049 and 07/688,138disclose methods of preparing biomedical electrode constructions in acontinuous strip subassembly.

For example, one method of continuous strip assembly can be the coatingof an aqueous mixture of crosslinked poly(N-vinyl pyrrolidone),polyethylene glycol, and potassium chloride on an electricallyconductive surface about 8.9 cm wide, with the coating applied to aboutthe center 5.1 cm section of such width. After evaporation of solvent,the coated electrically conductive surface can be bisected along thestrip and also cut orthogonally at about 2.54 cm intervals, yielding anumber of electrodes 10 seen in FIG. 1 having dimensions of about 2.54cm×4.4 cm with a conductive interface portion 18 of 2.54 cm×2.54 cm anda tab portion 20 of 2.54 cm×1.9 cm.

A further description of the invention may be found in the followingexamples using the following experimental procedures.

EXAMPLES Example 1

Approximately 100 grams of noncrosslinked poly(N-vinyl pyrrolidone)commercially available from BASF of Parsippany, N.J. in a solid stateform of particles having a size from about 10 micrometers to about 75micrometers were placed in a resealable plastic bag, purged withnitrogen for 15 minutes, irradiated with gamma radiation of 155 kGysusing a cobalt-60 high energy source to produce crosslinked solidpoly(N-vinyl pyrrolidone).

A mixture was prepared in which 9 grams of crosslinkedpoly(N-vinyl-2-pyrrolidone) homopolymer was added to a solutionconsisting of 18 grams of glycerin, 0.1 grams potassium chloride and 90grams of water. The mixture was stirred until equilibrated, at whichtime, the mixture was coated onto a 5.1 cm center strip of an 8.9 cmliner silver coated with E1700 silver ink from Ercon, Inc. of Waltham,Mass. The coated strip was dried in an oven at 66° C. for 30 minutes toessentially evaporate the water. A biomedical electrode having theresulting solid state conductive polymer composition on thesilver-coated liner was made by cutting an electrode having a conductiveportion of 2.54 cm×2.54 cm and a tab portion of 2.54 cm×1.9 cm, testedto determine impedance on a human arm.

Alternating current impedance was measured Measurements were made usingan Xtratek ET-65A ECG electrode tester from Xtratek Company of Lenexa,Kans. and conducted in the conventional manner on electrode pairsconnected "back-to-back" (adhesive-to-adhesive) using a low level signalsuitable for measurements on ECG electrodes. The impedance at 10 Hz wasrecorded. For skin impedance, twelve panelists were evaluated usingbiomedical electrodes prepared according to this Example 1 placed on thepanelists' arms and measured for alternating current impedance in kOhmsat a frequency of 10 Hz using a 4800A Vector Impedance Metermanufactured by Hewlett Packard of Palo Alto Calif. The Association forthe Advancement of Medical Instrumentation (AAMI) has adopted acceptablealternating current impedance at a frequency of 10 Hz to be less than2000 Ohms for "back-to-back" alternating current electrode impedance.Less than about 500 kOhms has been found acceptable for human skinimpedance. The performance of the electrodes for skin impedance islisted below in kOhms at time intervals of 0 minutes, 6 minutes and 12minutes. Table 1 shows the average of the results.

                  TABLE 1                                                         ______________________________________                                                  kOhms at     kOhms at kOhms at                                      Sample    T.sub.0 min. T.sub.6 min.                                                                           T.sub.12 min.                                 ______________________________________                                        Example 1 293          211      198                                           Example 2 254          206      201                                           ______________________________________                                    

Example 2

A solid state conductive polymer composition was prepared according toExample 1 except that the composition consisted of 9 grams ofcrosslinked poly(N-vinyl-2-pyrrolidone), 18 grams of 400 MW polyethyleneglycol, and 0.1 grams of potassium chloride. Table 1 shows the resultsfor alternating current impedance for electrodes according to Example 2on human arms using 16 people using the procedures according to Example1.

Samples prepared according to Example 2 above were placed in openenvelopes to determine shelf life effects on the performance of theelectrodes of the present invention. Samples of electrodes were testedat the following time intervals: both at room temperature initially,after 3 days, 1 week, 2 weeks, 4 weeks, and 8 weeks; and at 49° C. after4 weeks and after 8 weeks. Human skin impedance was measured using aHewlett-Packard 4800 A Vector Impedance Meter. Direct current offset andback-to-back alternating current impedance were measured using anXtratek ET-65A ECG electrode tester from Xtratek Company of Lenexa,Kans. Skin adhesion was measured by applying biomedical electrodes onthe back of human subjects and rolled with a 2 kg roller to insureuniform application. Electrodes were removed from the back promptlyafter application using a mechanical pulling device, consisting of amotor driven screw drive which pulls a 11.4 kg test line to which isattached a 2.54 cm wide metal clip. The metal clip is attached to eachelectrode at its 2.54 cm width during pulling testing. Electrodes werepulled in a plane parallel (180°) to the back at a rate of 13-14 cm/min.The adhesion data is reported in grams/2.54 cm and based on an averageof values from initiation of peel to entire removal of the electrode.

The results from this study are shown in Table 2 below. Direct CurrentOffset was within the AAMI Standard of less than 100 mvolt throughoutthe test duration. Impedance was within the AAMI standard of less than2000 Ohms throughout the test duration. Skin impedance at each intervalthroughout the test duration was less than 500 kOhms.

                                      TABLE 2                                     __________________________________________________________________________    CONDUCTIVE POLYMER COMPOSITION ELECTRODES                                             Direct     Skin  Skin  Skin                                                   Current    Impedance                                                                           Impedance                                                                           Impedance                                                                           Skin                                         Aging                                                                             Offset                                                                             Impedance                                                                           (kOhms)                                                                             (kOhms)                                                                             (kOhms)                                                                             Adhesion                                 Time                                                                              Temp.                                                                             (mV) (Ohms)                                                                              t = 0 min.                                                                          t = 6 min.                                                                          t = 12 min.                                                                         (grams)                                  __________________________________________________________________________    initial                                                                           --  0.9  586   254   206   201                                            3 day                                                                             RT  1.8  507   356   303   283   53                                       1 wk                                                                              RT  1.5  311   313   265   244   64                                       2 wk                                                                              RT  1.9  414   375   304   285   52                                       4 wk                                                                              RT  1.2  457   325   249   251   61                                       4 wk                                                                              49° C.                                                                     1.4  580   370   277   256   137                                      8 wk                                                                              RT  0.1  404   334   291   262   38                                       8 wk                                                                              49° C.                                                                     0.3  260   311   232   202   127                                      __________________________________________________________________________

Each DC offset and alternating current back-to-back electrode impedancevalue listed is an average of 16 pairs of electrodes. Skin alternatingcurrent impedance and skin adhesion values reported are averagesobtained from panels consisting of 24 data points.

Solid state conductive polymer compositions had a DC offset which isbelow 2 mV consistently throughout the test period of 8 weeks.

Skin adhesion for the electrodes aged at room temperature was quiteconsistent except for the sample at 8 weeks where there was a decreasein adhesion. Skin adhesion increased upon aging at elevatedtemperatures. Skin alternating current impedance for electrodes did notchange dramatically over the aging period.

Examples 3-7

Skin alternating current impedance and skin adhesion values for solidstate conductive polymer compositions were measured for ranges offormulations in which the ratio of solvating polymer: essentiallynon-volatile plasticizer: ionic salt varied from 46:51:3 weight percent,respectively, to 26:71:3 weight percent, respectively. Each of theformulations were prepared in accordance with Example 2. Crosslinkedpoly(N-vinyl pyrrolidone) (PVP) prepared according to Example 1 was thesolvating polymer. Polyethylene glycol (400 Molecular Weight) was theessentially non-volatile plasticizer. Potassium chloride was the ionicsalt. Table 3 reports the results of the average 16 data acquisitionsfor each of the examples shown in Table 3. The data in Table 3 suggestthat a preferred formulation considering both skin impedance and skinadhesion values is about 32 weight percent solvating polymer, 65 weightpercent non-volatile plasticizer and about 3 weight percent ionic salt.

                                      TABLE 3                                     __________________________________________________________________________                  Skin  Skin  Skin  Alternating                                                 Impedance                                                                           Impedance                                                                           Impedance                                                                           Current                                                                             Skin                                         %  %  %  (kOhms)                                                                             (kOhms)                                                                             (kOhms)                                                                             Impedance                                                                           Adhesion                                Example                                                                            PVP                                                                              PEG                                                                              KC1                                                                              t = 0 min.                                                                          t = 6 min.                                                                          t = 12 min.                                                                         (Ohms)                                                                              (grams)                                 __________________________________________________________________________    3    46 51 3  370   308   298   >3000*                                                                              31.3                                    4    37 60 3  268   205   201   255   56.4                                    5    32 65 3  196   215   206   244   67.9                                    6    29 68 3  177   173   169   246   78.8                                    7    26 71 3  194   158   155   237   70.7                                    __________________________________________________________________________     *Exceeded limit because insufficient adhesion to perform this test betwee     the two electrodes.                                                      

Examples 8-14

Electrodes were prepared according to Example 2, except that the amountof the weight percent of ionic salt was varied from about 0.5 weightpercent to about 5 weight percent potassium chloride. The remaining99-95 weight percent, respectively, consisted of a constant ratio of 32weight percent poly(N-vinyl-2-pyrrolidone) and 65 weight percentpolyethylene glycol (400 M.W.).

Skin impedance data was collected in accordance with the procedures ofExample 5. Table 4 reports the results.

                  TABLE 4                                                         ______________________________________                                                        Skin       Skin     Skin                                                      Impedance  Impedance                                                                              Impedance                                         %       (kOhms)    (kOhms)  (kOhms)                                   Example KC1     T = 0 min. T = 6 min.                                                                             T = 12 min.                               ______________________________________                                        8       0.5     290        243      235                                       9       1.0     271        229      217                                       10      1.5     259        218      208                                       11      2.0     262        215      203                                       12      2.5     269        223      212                                       13      3.0     257        210      201                                       14      4.0     283        226      296                                       ______________________________________                                    

From a comparison of the results of Examples 3-7 with the results ofExamples 8-14, the presently preferred formulation of solid stateconductive polymer composition of the present invention comprises 33weight percent crosslinked poly(N-vinyl pyrrolidone), 65 weight percentpolyethylene glycol, and 2 weight percent potassium chloride.

Example 15

To 100 gram of water was added 8.9 gram of polyacrylamide (molecularweight, 5 million) commercially available from American Cyanamid ofWayne, N.J. and 2 grams of potassium chloride. The mixture was allowedto swell overnight. Glycerin (89 grams) was added to the swollen mixtureand the final mixture was homogenized. The mixture was coated 0.5 mmthick onto a silver conductive backing and dried at 66° C. for 20minutes. Electrodes were prepared by cutting the material into 2.54cm×3.81 cm rectangular strip where the top 2.54 cm×2.54 cm area wascoated with the mixture, leaving a tab portion of 2.54 cm×1.27 cm ofexposed silver conductive material. A pair of electrodes were connectedadhesive to adhesive (back to back) and found to have a D.C. offsetvalue of 0.1 mV and electrode impedance of 100 Ohms. The average skinimpedance tested on human arms of 3 volunteers was 189 kOhms.

Example 16

To 3.4 grams of glycerin was added 34 grams ofpolyacrylamido-2-methyl-propanesulfonic acid, sodium salt, (10% solidsin water, commercially available from Aldrich of Milwaukee, Wis.)Potassium chloride (0.2 grams) was then added to the mixture and upondissolution, the solution was coated at 0.5 mm onto a silver backing anddried in an oven at 66 degrees C. for 15 minutes. Electrodes wereprepared according to Example 15. Back-to-back alternating currentimpedance was determined to be 65 Ohms, DC offset of 9.4 mvolts, andaverage skin impedance of 275 kOhms averaging results from nine humansubjects.

Example 17

To prepare a composition which was cohesive and pliable but notpressure-sensitive adhesive, a mixture was prepared in which 5.5 gramsof noncrosslinked poly(N-vinyl-2-pyrrolidone) homopolymer (K-90commercially available from BASF of Parsippany, N.J.) was added to asolution consisting of 10.8 gram of polyethylene glycol (Pluracol E400,400 M.W. commercially available from BASF), 15 grams of water and 0.33grams of potassium chloride. The mixture was stirred until equilibrated.The mixture was then coated at 0.5 mm onto a silver liner and dried for15 minutes at 66° C. Electrodes were prepared according to Example 15.Alternating current impedance was 1016 Ohms. DC offset was 3.3 mVolt.Average skin impedance was 141 kOhms averaging results from ninesubjects.

Example 18

Polyacrylic acid, 10 grams (1,000,000 MW; commercially available fromAldrich), was added to 50 grams of glycerin, 80 grams water and 1.4grams of potassium chloride. The mixture was stirred and allowed toequilibrate. The mixture was coated onto silver backing at 0.5 mm andthen dried at 66° C. for 15 minutes. Electrodes were prepared asdescribed in Example 15. Alternating current impedance was 118 Ohms. DCoffset was 0.5 mVolts. An average skin impedance was 164 kOhms usingnine subjects.

Example 19

Three samples were prepared with polyacrylic acid, two of which wereneutralized with NaOH. The samples were prepared by dissolving 0.25 g ofpotassium chloride in 30.0 g water followed by the addition of 10.0 gglycerin. Noncrosslinked polyacrylic acid 1.0 g (Aldrich; 1,000,000 MW)was then added to the solution and the resulting mixture wasequilibrated for 2 hours. One sample was not neutralized. The secondsample was approximately 50% neutralized by the addition of 0.66 g of a50% by weight aqueous NaOH solution. The third sample was approximately100% neutralized with the addition of 1.12 g of a 50% by weight aqueousNaOH solution. Electrodes were prepared from these solutions accordingto the manner described in Example 15. Table 5 shows the results ofimpedance and voltage measurements.

                  TABLE 5                                                         ______________________________________                                                        AC                                                            Sample          Impedance D.C. Offset                                         % Neutralized   (Ohms)    (m volt)                                            ______________________________________                                        0               34        -0.3                                                50              10        -0.1                                                100             31        -0.4                                                ______________________________________                                    

Example 20

To 67.4 grams of glycerin was added 2.5 grams of KCl. The salt solutionwas mixed in a shaker for 15 hours. In a separate vessel was combined 30grams of N-vinyl-pyrrolidone, 0.02 grams of diallyl maleate crosslinkingagent, and 0.06 grams of 2,2-dimethoxy-2-phenylacetophenonephotoinitiator (benzildimethylketal commercially available as "Irgacure651" from Ciba Geigy). The two mixtures were mixed together and curedunder blacklight (350 nm lamp available from Sylvania) operated at a 1.2milliwatts/cm² intensity in a nitrogen atmosphere for four minutes insheet form. Electrodes were constructed by laminating the curedconductive adhesive onto a silver-lined backing, having a conductiveportion of 2.54 cm×2.54 cm. The back-to-back impedance was 400 Ohms. TheDC offset was 0.8 mV.

Example 21

Electrodes were prepared according to Example 2, except that theplasticizer was polyethylene glycol (300 molecular weight). Theelectrodes were incubated in humidity chambers at 60% humidity at 37° C.and 90% humidity at 49° C., respectively. The electrodes were weighedbefore and after the incubation period. Water uptake expressed inpercentage water content based on adhesive weight was calculated. Theelectrical properties of these electrodes were evaluated according toAAMI standards. Results are shown in Table 6.

                  TABLE 6                                                         ______________________________________                                                                        AC                                                      Percent     DC Offset Impedance                                     Electrodes                                                                              water       mV        (Ohms)                                        ______________________________________                                        control, no                                                                   incubation            0.1       95                                            1         3           2.4       66                                            2         34          0.6       59                                            3         48          0.4       3                                             ______________________________________                                    

These results show that solid state conductive polymer compositions ofthe present invention are ionically-conductive regardless of the amountof water present during storage or use.

Examples 22 and 23

A solution of polyvinylmethylether (50% by weight in water) was obtainedfrom Aldrich Chem. Co. To 16.05 grams of this solution was added 0.4grams of lithium chloride and 5.6 grams of water. Because thecomposition was cohesive and pliable, no non-volatile plasticizer wasrequired. The composition was spread onto the silver conductive backingas described in Example 15 and dried to prepare an electrode. The ACimpedance of this electrode was determined to be 4 Ohms and a DC offsetof 0.0 mV.

Another sample was prepared in which 23 gram of the polyvinylmethylether solution was charged with 2 grams of glycerin, 0.53 grams ofpotassium chloride and 11.08 grams of water. A cohesive and pliablesolid state conductive polymer composition formed after drying on asilver coated backing to form an electrode as described in Example 15.The AC impedance was determined to be 2 Ohms and DC offset of 0.0 mV.

Example 24

A copolymer system was prepared consisting of polyacrylamide andpoly(vinyl alcohol) (PVA). The PVA was added to increase cohesiveproperties of the polyacrylamide. A polyacrylamide solution consisted of10 grams of polyacrylamide, 60 grams of glycerin, 2 grams of KCl and 100grams of water. A PVA solution was prepared by dissolving 10 grams ofPVA (88% hydrolyzed, from Aldrich Chemical) into 70 grams of boilingwater with constant stirring, followed by the addition of 20 grams ofglycerin. A copolymer mixture was prepared by mixing 10 parts by weightof the polyacrylamide solution to 1 part by weight of the PVA solution.The mixture was coated 0.5 mm thick onto a silver conductive backing anddried at 66° C. for 20 minutes. An electrode was prepared in the manneraccording to Example 15. The AC impedance was 163 Ohms and DC offset was0.5 mV.

Example 25

A solid state conductive polymer composition was coated from an aqueousmixture consisting of 25% adhesive solids. A vessel was charged with11,250 g water and 75.0 g of potassium chloride and then mixed untildissolution. Then 2,437.5 g of PEG 400 (Carbowax brand, Union Carbide)was added and the mixture was stirred until rendered homogeneous.Poly(N-Vinyl-2-pyrrolidone) particles (1,237.5 g of BASF K-90),crosslinked with 155 kGys of gamma radiation in a nitrogen atmosphere)was then added to the mixture and then stirred vigorously for 30 minuteswith a high viscosity mixer. The drum was sealed with a plastic bag andthen set overnight to equilibrate. After setting for 24 hours themixture was stirred again and the resultant mixture was ready forcoating.

Coating equipment was provided with a knife over bed coater and a dryingoven employing 3 total passes, each pass being 3.05 m in length. Thethree passes were drying passes, each employing a temperature controlunit. The adhesive mixture was coated onto a low release polyethyleneterephthalate backing (having a Ag/AgCl ink commercially available fromErcon Inc. coated thereon). The adhesive was between 0.8 mm and 1.0 mmthick. Line speed was 1.9 m/min. The temperature of the three dryingpasses were 121° C., 121° C., and 60° C., respectively.

Glass Transition Temperature Comparison Study

Glass transitions were determined to demonstrate the susceptability ofcommercially available polyelectrolyte containing biomedical electrodesto dry out as compared with bioelectrodes containing solid stateconductive polymer compositions of the present invention. An increase inglass transition temperature indicates a loss of water in the adhesivecomposition. The glass transition temperatures of a number ofcommercially available electrodes and electrodes prepared according tothese Examples were measured according to the following procedure:

Glass Transition Temperature

The glass transition temperatures reported were measured incorporating aMettler TA3000 System commercially available from Mettler InstrumentCorporation of Hightstown, N.J. The system employs a Mettler TC 10Processor, a Mettler Differential Scanning Calorimeter (DSC) 30 lowtemperature cell, and a Minnesota Valley Engineering (MVE) liquidnitrogen reservoir. A sample of adhesive was placed into a 40 microliteraluminum crucible (ME-27331 also from Mettler). The crucible was thenplaced into a Mettler DSC low temperature cell. The low temperature cellwas connected to a MVE cryogenics model LAB 50 vessel, which was filledwith liquid nitrogen. DSC thermal analysis was then measured from 50° C.to -140° C. at a rate of 10° C./minute. The glass transition was thendetermined from the DSC thermal analysis and is reported in Table 6 in°C. The values reported are midpoint values obtained from the DSC curve.

Table 7 compares glass transition temperature for commercially availablepolyelectrolyte biomedical electrodes and biomedical electrodes of thepresent invention measured initially and after being exposed toatmospheric conditions for 14 days. Glass transition temperatures werealso determined for the electrodes dried at 66° C. for 15 minutessimulating the drying conditions of the solid state conductive polymercomposition during processing of the composition. In this instance,electrodes from Examples 1, 15, 17, 18, and 21-23 were reheated to thesame temperature for the same duration as employed for preparation ofsuch electrodes initially.

Table 8 shows skin impedance on human arms and back-to-back alternatingcurrent electrode impedance.

                  TABLE 7                                                         ______________________________________                                                                            Tg,                                                                  Tg,      drying                                                       Tg,     aging    65° C., 15                         Conductive Adhesive Composition                                                                  initial 2 weeks  min                                       ______________________________________                                        Q-Trace ™ Electrode.sup.1                                                                     -98.5*  -68.5    -70.4                                     Fastrace 4 ™ Electrode.sup.2                                                                  -88.4*  -70.7    -74.9                                     Tracets AG 4000 ™ Electrode.sup.3                                                             -84.5*  -70.7    -75.7                                     Tracets MP 3000 ™ Electrode.sup.3                                                             -84.2*  -70.3    -73.7                                     Signal ™ Electrode.sup.4                                                                      -96.9*  -76.7    -80.1                                     Example 1          -83.2   --       -81.3                                     Example 15         -86.4   --       -82.3                                     Example 17         -66.5   --       -65.8                                     Example 18         -86.2   --       -80.6                                     Example 21         -71.1   -72.9    -68.3                                     Example 22         -31.8   --       -28.0                                     Example 23         -32.9   --       -29.9                                     ______________________________________                                         .sup.1 Commercially available from Graphic Controls, Medi-trace Products      Div., Buffalo N.Y.                                                            .sup.2 Commercially available from Medtronic Andover Medical, Haverhill,      Massachusetts                                                                 .sup.3 Commercially available from Lectec Corporation, Minnetonka,            Minnesota                                                                     .sup.4 Commercially available from Minnesota Mining and Manufacturing         Company, St. Paul, Minnesota                                                  *Initial testing promptly after removal from protective packaging        

                                      TABLE 8                                     __________________________________________________________________________                         AC Impedance,                                                                          Skin Impedance,                                             DC offset mV                                                                           Ohms     kOhms                                           Electrodes  T, initial                                                                         T, 2W                                                                             T, initial                                                                         T, 2W                                                                             T, initial                                                                         T, 2W                                      __________________________________________________________________________    Example 21  1.0  3.3 143  255 153  230                                        Signal ™ Electrode                                                                     0.1  0.4 149  674 135  553                                        Tracet Ag 4000 ™                                                                       0.0  0.6 940  3700                                                                              364  860                                        Electrode                                                                     Tracet MP 3000 ™                                                                       0.2  1.1  68  1186                                                                              277  677                                        Electrode                                                                     Fastrace 4 ™                                                                           0.1  0.1 623  935 216  456                                        Electrode                                                                     Q-Trace ™ Electrode                                                                    2.1  0.1 467  878 140  650                                        __________________________________________________________________________

The changes in glass transition temperatures of the electrode samplescommercially available demonstrate a sensitivity of these systems to aloss of water. By contrast, the glass transition temperature of eachpolymer electrolyte electrode containing a solid state conductivepolymer composition of the present invention did not change essentiallyafter 14 days or after a second heating at 65° C. for 15 minutes,because the solid state conductive polymer composition of the presentinvention did not contain water or other volatile plasticizerssusceptible to evaporation. Thus, ionic conductivity of solid stateconductive polymer compositions of the present invention are retainedafter exposure to atmospheric conditions.

The present invention is not limited to the above embodiments. For anappreciation of the scope of the present invention, the claims follow.

What is claimed is:
 1. A solid state conductive polymer compositioncomprising:(a) an ionically conductive polymer electrolyte complexformed by a process where the complex is effectively dehydrated byessentially evaporating water, and (b) optionally if the complex is notcohesive and pliable, an essentially non-volatile plasticizer present inan amount of from about 0 to about 95 weight percent of the composition;said polymer electrolyte complex comprising a solid solution of an ionicsalt dissolved in a solvating polymer wherein the complex is ionicallyconductive after processing; said solvating polymer present in an amountof from about 5 to about 98 weight percent of the composition; saidionic salt present in an amount of from about 0.5 to about 5 weightpercent of the composition; said solvating polymer comprisingpolyacrylamide and its ionic forms; polyacrylic acid and its salts;poly(vinyl alcohol); poly (vinyl methyl ether);poly(2-acrylamido-2-methylpropane sulfonic acid), its salts, copolymersof the acid, copolymers of salts of the acids, or mixtures thereof, orcombinations thereof; wherein the composition maintains its glasstransition properties and maintains its alternating current impedanceproperties below 2000 Ohms notwithstanding exposure to ambient airconditions for at least two weeks.
 2. The composition according to claim1, further comprising an iontophoretically active pharmaceuticalassociated with the composition.
 3. The composition according to claim1, wherein said solvating polymer comprises crosslinked polyacrylamideand its ionic forms; crosslinked polyacrylic acid and its salts;crosslinked poly(2-acrylamide-2-methylpropane sulfonic acid), its salts,crosslinked copolymers of the acid, crosslinked copolymers of salts ofthe acid, or mixtures thereof; or combinations thereof; and wherein theplasticizer is present in an amount of from about 65 to about 95 weightpercent of the composition to form a cohesive, pliable andpressure-sensitive adhesive composition.
 4. The composition according toclaim 1, wherein said ionic salt comprises lithium chloride, lithiumperchlorate, sodium citrate, potassium chloride, or mixtures thereof. 5.The composition according to claim 4, wherein said ionic salt ispotassium chloride present in an amount of from about 2 to about 3weight percent of the composition.
 6. The composition according to claim1, wherein said plasticizer is a polyhydric alcohol comprising glycerin,polyethylene glycol, or mixtures thereof.
 7. The composition accordingto claim 5, wherein said plasticizer is polyethylene glycol present inan amount of about 65 weight percent of the composition.